1. Field of the Invention
The present invention relates to a vacuum processing device and particularly relates to improvements in a sputtering apparatus.
2. Description of Related Art
Reference numeral 101 in FIG. 8 shows a related sputtering apparatus. This vacuum processing device 101 has a vacuum chamber 111.
An exhaust opening part 118 is provided at the vacuum chamber 111. The exhaust opening part 118 is connected to a vacuum exhaust system (not shown) so that when the vacuum exhaust system is driven, the contents of the vacuum chamber 111 can be evacuated.
A gas introduction opening part 117 is provided at the vacuum chamber 111. This gas introduction opening part 117 is connected to a gas introduction system (not shown). Gas can also be introduced to the inside of the vacuum chamber 111 from the gas introduction opening part 117.
A backing plate 112 is located at the ceiling of the vacuum chamber 111 and a target 113 consisting of a dielectric material is located at a side of the backing plate 112 facing the inside of the vacuum chamber 111.
A mounting table 115 facing the target 113 is located at the inside bottom surface of the vacuum chamber 111. The surface of the mounting table 115 is flat and a substrate can be mounted on this surface as described later.
A radio-frequency supply 114 is provided at the outside of the vacuum chamber 111. This radio-frequency supply 114 is connected to a backing plate 112 so that when the radio-frequency supply 114 is activated, radio-frequency power can be supplied to the target 113 via the backing plate 112.
In order to form a thin film of dielectric using sputtering techniques on a surface of a silicon substrate using a sputtering apparatus 101 of this configuration, first, the inside of the vacuum chamber 111 is evacuated, and a substrate 120 is transported towards the inside of the vacuum chamber 111 and mounted on the surface of a mounting table 115 while maintaining a vacuum atmosphere. The potential of the substrate 120 is floating at this time.
Next, a discharge occurs when radio-frequency power is supplied to the target 113 while introducing a constant amount of sputtering gas such as Argon gas etc. from the gas introduction opening part 117. An adhesion preventing plate 119 is connected to earth so that the discharge occurring within the vacuum chamber 111 is stable.
When discharge occurs, the target 113 is sputtered. At this time, in addition to flying off in the direction of the surface of the substrate 120, the sputtered target material also flies off in the direction of the side surface of the inside of the vacuum chamber 111 and in the direction of the inner bottom surface. However, an adhesion preventing plate 119 formed substantially in a semi-spherical shape with a circular opening part in the bottom thereof is provided on the inside of the vacuum chamber 111. The opening part in the bottom of the adhesion preventing plate 119 is positioned close to the mounting table 115, with the target 113, side surface within the vacuum chamber 111 and the inner bottom surface being partitioned by the adhesion preventing wall 119 so that the sputtered target material does not become directly attached to the inside bottom surface or inside side surface of the vacuum chamber 111. A thin film is then formed on the surface of the substrate 120 from target material reaching the surface of the substrate 120.
However, according to the sputtering apparatus of the above configuration, in particular, while a thin film of dielectric is being formed, when a plurality of films are formed on the substrate consecutively, the distribution of the thickness of the film on the substrate surface and the film-deposition speed change. Discharge therefore cannot be maintained due to discharge becoming unstable when deposition of thin films is continued.
In order to resolve the aforementioned problems of the related art, it is therefore the object of the present invention to provide technology where, when depositing thin films using sputtering techniques, discharge is stable and film deposition speed and film thickness distribution are uniform even in cases where a plurality of dielectric films are formed consecutively on a substrate.
In order to resolve the aforementioned problems, in a first aspect of the present invention, a sputtering apparatus comprises a vacuum chamber, a target positioned within the vacuum chamber, a substrate support, located within the vacuum chamber opposite the target, capable of supporting the substrate, and an opposing electrode connected to earth located about the periphery of the substrate support with a surface thereof facing the target, the surfaces being uneven.
With a second aspect of the present invention, the opposing electrode has a through-hole at the center thereof, and the substrate support is located within the through-hole.
In a third aspect of the present invention, the unevenness is comprised of a plurality of holes formed in the surface of the opposing electrode for the sputtering apparatus according to the first aspect.
A fourth aspect of the present invention is the sputtering apparatus according to the third aspect, wherein the depth of the holes is at least twice the diameter of the holes.
In a fifth aspect of the present invention, with the sputtering apparatus according to the first aspect, the target is positioned on the side of the inside ceiling of the vacuum chamber; the opposing electrode being located at an inner bottom side of the vacuum chamber; and wherein the surface of the opposing electrode is inclined in such a manner that the height of the outer side is lower than the height of the inner side.
With a sixth aspect of the present invention, for the sputtering apparatus according to the fifth aspect, the surface of the opposing electrode is inclined by at least 10xc2x0 with respect to a horizontal plane.
In a seventh aspect of the present invention, the target for the sputtering apparatus according to the first aspect is a dielectric selected from the group consisting of BaTiO3, SrTiO3, (BaSr)TiO3, Pb(ZrTi)O3, and SrBi2Ta2O9.
In an eighth aspect of the present invention, with the sputtering apparatus according to the first aspect, only the opposing electrode is connected to earth within the vacuum chamber.
With the related sputtering apparatus described above, when a thin film of dielectric is formed, when films are formed consecutively, the distribution of the thickness of the film on the substrate surface and the film-deposition speed change, thereby causing discharge to become unstable when forming of films is continued. The inventor conceived the present invention in order to overcome a problem where, when dielectric becomes affixed to the surface of an adhesion preventing plate located in a position close to the target or substrate during sputtering, so that a dielectric film is formed, positive charge becomes affixed to the surface of the dielectric film, and the charge distribution density of positive charge occurring at the surface of the adhesion preventing plate becomes large, the potential of the surface of the adhesion preventing plate can no longer be held at earth potential and the discharge therefore becomes unstable.
The sputtering apparatus of the present invention is conceived based on this concept and is therefore provided with an opposing electrode, held at earth potential, with a surface that is made uneven as a result of forming, for example, a plurality of holes in the surface, with the opposing electrode being located at a position at the periphery of the mounting table within the vacuum chamber. Target material therefore does not become directly attached to the inner bottom surface of the vacuum chamber when the target is sputtered because the target material instead becomes affixed to the adhesion preventing plate and the opposing electrode.
Further, the surface area of the opposing electrode is large because a multiplicity of holes are formed at the surface of the opposing electrode. Sputtered dielectric material therefore becomes affixed to the surface of the opposing electrode and to the inside of the holes so that a dielectric film is formed at this surface. The charge density of distributed charge is therefore small compared with the related art even when positive charge is distributed at the dielectric film because the surface area of the opposing electrode surface is large. The potential of the opposing electrode surface can therefore be kept substantially at earth potential.
Discharges within the vacuum chamber are therefore stable compared with the related art even when dielectric films are consecutively formed because the potential of the surface of the opposing electrode is kept substantially at earth potential. It is therefore difficult for the fluctuations in film thickness distribution and film deposition speed and instabilities in the discharges that occur in the related art to occur.
When a plurality of shallow holes are formed in the opposing electrode, the surface area of the opposing electrode is small compared to when the holes are deep. When a large number of substrates are then processed, there are cases where the potential of the opposing electrode surface cannot be held at earth potential. However, in the present invention, a multiplicity of deep holes where the depth of the holes is two times or more greater than the diameter of the holes are formed. The surface area of the opposing electrode is therefore large compared to the case where holes are not formed. The potential of the surface of the opposing electrode can therefore be maintained at earth potential for a long period of time and the discharge can be maintained in a stable manner for a long period of time.
In the present invention, the surface of the opposing electrode is inclined in the direction of the side surface on the inner side of the vacuum chamber.